MUSE - Towards A Supercomputer

In 1956 Kilburn decided to start building yet another machine - MUSE - using junction transistors. This was to be really powerful, the first supercomputer of its era. It was perhaps the technical triumph of the Manchester design team. The Mark I had introduced index registers - an indispensable tool in programming. The MUSE added to this the idea of virtual paged memory. Something that we are only just getting used to on desktop machines. The idea was that you could simulate additional memory by writing out pages that weren’t needed and reusing the resulting free memory. Of course the cost of this approach is that you have to read the page back in if it is needed again and this slows things down.

A sort of paging system had been implemented in software in the Mark I’s high level language - but in MUSE the paging was built into hardware. It made use of a content addressable memory that today we would describe as an address-translation look-aside buffer. There was even a “drum learning” program which organized the page replacement strategy in fast ROM. This might even represent the first use of AI techniques in a machine!

Perhaps even more important that the virtual paged memory hardware was the fact that the MUSE was the first machine to be designed taking the needs of the operating system into account. It had 128 24-bit addressing registers. Of these application programs could use 90. The rest were for the operating system. Instructions addressed memory using an offset which was added to any two of the base registers. A program could maintain the base address, offset and bounds of a data structure within the registers. The problem with having so many registers is that they all had to be saved when the processor switches its attention to another running task.

MUSE did its best to make such context switches fast. It had three program counters - one for users, one for the operating system and one for the hardware based “extra code” routines that extended its instruction set. The 37 addressing registers dedicated to the operating system were used to keep track of running programs and were not swapped. MUSE was also a pipelined machine, with vectored interrupts and interleaved memory. It would be easily understood by a modern computer designer except for one thing - it was an asynchronous machine and had no central clock.

MUSE becomes Atlas

The MUSE was taken up by Ferranti who were convinced by the Mercury that what the world really needed was a scientific super computer. The new machine was called the Atlas and it could claim to be the fastest and most sophisticated computer in the world. Manchester had leap frogged the USA in computer design - but the companies like Control Data Corporation (CDC) were catching up. The published material on the MUSE was read carefully by Seymour Cray, CDC’s chief designer, who then went on to create the CDC 6600 - a more powerful and more successful machine than the Atlas.

The Atlas control panel

The Manchester Altlas was the first of production versions. Ferranti sold only two other of these machines. One went to the University of London which purchased it jointly with BP the other to the UK Science Research Council which was installed in a purpose-built Atlas Computer Laboratory at Chilton for use by government agencies and universities.

Chilton Atlas

Ferranti did go on to build the Atlas 2 - surprisingly with help from Cambridge University. Only one Atlas 2 was ever sold and Ferranti decided to give up the field in 1962 when the sold out to ICT - later to become ICL. ICT decided to concentrate on there 1900 range of commercial machines and the Atlas was scrapped.